This trait provides behavior missing from jdk 1.6, 1.7, see:
sadly depends on unsupported implementation classes,
(com.sun.tools.javac.*). As a result, this may stop working on on
Java 9. At that point we can either:
1) Take the long way around and find Elements ourselves by searching the
scope/target for the selected name (see my older version of JavaDocFinding).
2) Use reflection here.
3) Convince Java 9 to let us import these unsafe libs.